In digital terrestrial television broadcasting that transmits digitized image and sound signals based on ground waves, a broadcast signal band is split into thirteen segments and used. By using one of these segments, broadcasting called one-segment broadcasting mainly for mobile units has been put into practice. The receiving function of the one-segment broadcasting is introduced into not only dedicated television receivers but also information devices such as personal computers and portable telephones.
In the one-segment broadcasting, other than images and sounds of ordinary TV programs supplied through the ground waves from broadcasting stations, data broadcasting that supplies information via a network such as the Internet is implemented as a supplementary service. In the data broadcasting, link information is included in the information which has been transmitted through the ground waves from the broadcasting stations. This link information indicates a content that may be accessed through the Internet and is in the data broadcasting server. A user device that functions as a television receiver on the user side acquires the link information from the received ground waves, obtains the content according to the link information from a data broadcasting server, and displays the content. The content provided by the data broadcasting server includes not only texts but also images and sounds. In the one-segment broadcasting, there may be performed on-demand information provision according to a user's operation, beyond constraints of programs provided based on broadcast waves.
In the data broadcasting, there is desired a service that makes use of the feature of on-demand information provision and thereby providing special contents only to specific users. Conventionally, in network distribution only by communications among computers connected via a network, and CS (Communications Satellite) broadcasting as well as cable television broadcasting, a service called VOD (Video On Demand) and providing, for example, pay contents to user devices that have completed a charging procedure has been obtained.
In the VOD through the network, an administrative server, which is different from a contents server transmitting the contents, receives credit card information from a personal computer (PC) on the content receiving side, and transmits license information for descrambling by electronic mail. When the contents server transmits a content protected by scrambling or the like to the PC that is the user device on the reproduction side, the PC descrambles the content by using the acquired license information and displays the content.
Further, as a system of protecting special contents, there is known, for example, a system that applies DRM (Digital Rights Management) to a content to be supplied from a server to a user device and thereby limits the reproduction of the content (for example, see Japanese Laid-open Patent Publication No. 2004-342080). In this system, the user device transmits a digital signature to the server, and the server inserts the signature into a DRM message in the content.
Furthermore, in the CS broadcasting and the cable television broadcasting, when operation of selecting a pay content is performed by a user, this selection operation is accumulated in a built-in IC card as viewing data and the content is displayed. The viewing data accumulated in the IC card is made known to the distribution side by telephone line, for example.
In the CS broadcasting and the cable television broadcasting, users viewing the contents are limited and the IC card may be incorporated into every user device. However, in broadcasting, such as the one-segment broadcasting, in which users viewing the contents are not limited and PCs may be used as user devices, it is not realistic to newly incorporate IC cards and interfaces into all the user devices. Further, in the network distribution, a means of exchanging data with an administrative server by electronic mail and the like may be provided, making the configuration of the user device complicated. Furthermore, in the system using DRM, the DRM message is inserted into the content, and the content may be revised for every user device to change the signature in the DRM message. This makes the processing on the transmitting side complicated.